Electric demineralizing apparatus

ABSTRACT

An electric demineralizing apparatus and method in which porous electrodes of the same composition are located in compartments on opposite sides of an ion permeable membrane and the electrolyte flows through the electrodes and along the membrane. When a D.C. potential is applied across the electrodes, waste water is produced in one compartment and product water is produced in the other compartment. The D.C. power source drives electrons into one set of electrodes and extracts electrons from the other set of electrodes.

[111 3,755,135 [4 Aug. 28', 1973 United States Patent [191 Johnson [54] I ELECTRIC DEMINERALIZING APPARATUS 3,553,092 1/1971 Muno et 204/180 P Primary Examiner-John H. Mack Assistant Examiner-A. C. Prescott Attorney-Robert E. Geauque m o k a B 3 2 49 i m m mC ma 0d m. .v MR n mw AA n o t n e V n l m 7 .l

[22] Filed: Jan. 20, 1971 211 Appl. No.: 107391 ABSTRACT An electric demineralizing apparatus and method in 204/301, 204/180 P. 204/180 B Int. Field of Search.;...................

[52] US. [51] B01 d 13/02 which porous electrodes of the same composmon are 204/180 P, I80 B,

located in compartments on opposite sides of an ion permeable membrane and the electrolyte flows through the electrodes and along the membrane. When a DC.

[56] 7 References Cited potential is applied across the electrodes, waste water UNITED STATES PATENTS is produced in one compartment and product water is produced in the other compartment. The DC. power d n a d 00 t CC M 6 e r f H mm aw Sr 8 e.m mm w o m teD .m m s 9 nm 5 mm m tf m C l hnC mm C mm re d S we m m we XXXX BBPP 0000 8888 mmmm 0000 2222 Stavennan....

Johnson et al.

mm mm e. PR 6740 5567 9999 HHHH 9466 7944 0 76 ,3 3855 683 2233 I 4 ELECTRIC DEMINER'ALIZING APPARATUS 7 BACKGROUND OF THE INVENTION- A number of= processes have been utilized for the demineralizing of water, such as distillation; freezing,

electrodialysis and reverse osmosis. 'l he'electrodialysis process uses alarge chamber dividedinto compartments by thin plastic sheets or membranes. Two typesof membranes areused-L and they are placed alternatelyt One type allowsonly positive ions topass throughandthe other lets only negative-ions througli.

A positive electrode and a negative" electrode are placed in compartments onopposite: sides" of the de:

mineralizing compartment-- and' connected across a source of electricalpotential. When'anelectric current" is sent through the water, ,the negative." ions'are drawn through thenegativeion permeable membranes'toward the positive electrode and thepositive:ions are'drawm throughthe positiveionpermeable membranes-toward" the negative electrode. Freshwater is produced in al ternate compartments between the 'electrodecompart ments. In US. Pat: No. 315-1 ;664; assigned to the'same' assignee; .the fluid =electrolyte flows through permeable electrodes-which are alternatelyanion and cation col'- lecting' electrodes; insulatedtfrom one another by p'o'= rous separations. Theelectrodescan-consist of carbon 1 granules coated "with an -ion exchange material in fluid i form which .is-p'olymerized,-to render=the material insol uble; The adjacent electrodes are oppositely charged from .a-reversible source ofdirect current:

SUMMAR-Y OF THE INVENTION v The present inventionrelatesto an electric deminer alizingapparatus and? method: in whichporous electrodes of thesame composition are located on opposite sides of an ion permeable membrane. The electrodes can be of 'thesame composition asthose described 'in US; Pat: No. 3,5l5;664, or-theelectrodescan be pre-' pared by another process disclosedherein-, and the membrane. can be-either'apositive ion or negative ion permeable membrane of the kinds utilizedinelectrodialysis. The electrolyte flows throughtheelectrodes along the membranexand- 'when a--.potential is applied across the electrodes, brine is produced at'one electrode and.'product waterisproduced at the other elec-" trode: It is preferred to utilize an-anionpermeable membrane to separate cation responsiveelectrodes' since. an anion responsive electrode'has a tendency to degrade toward the cationform': However, asuitable apparatus can utilize anion responsive electrodesseparated by a cation permeable membrane.

Theelectrodes'can be arrangedin a stack -andsepa rated by a'pluralityv of membranes; with "all'even numbered electrodesconnected' electrically in parallel and all alternatev (odd numbered) electrodes 'also' connected in parallel. Manifolding is requiredto flow one electrolyte streamthrough the even-numbered electrodes-anda separatestream through"'theodd num-' terstitial water of I the first set of electrodes is desalted ('d e'mineralized) while the mineralization" of the water of the second set is increased. After a suitable period of time during which the respective streams of water through the twowater manifold systems are disposed of, the electric currentis'caused tobe'reversed, and the process isrepeated with a correspondi'ri'g reversal of the desalting effects of the two streams.

The transfer of one electron r'eriioiiesbotlifacation and an' anion from the product stream and adds an equivalent pair to the waste streani'wher'e'as' i'ritlie process ofUiS; Pat; No. 3 ,5 l5 ,664 the t'ran'sfefof two" electrons are required to produce the same results: Thus; one electron in the present invention is used twice as effectively.

of anion-permeable membrane;

FIG. 2"is a'schematic illustration "ofabasic apparatus showing: two electrodes formed of cation responsive carbon particles and-an anion permeable membrane therebetween;

FIG. 2a is'a reduced schematic illustration similar to FIG: 2 'showing'the two 'electi'odesforrned of anio'n responsive carbonparticles and a cation perr'rie'able' membran'ethereb'etween; Y

FIG: 3 is a schematic illustration of the electron ex change between the electrodes;

FIG. 4 ,is a diagrammatic illustration 'of a stack of similar electrodes which are separated bythe-'same typeof' membranes; and 7 FIG; 5 is-a schematic illustration sim'ilarto'FlG. 2 showing "anion responsive beads interspersed between the cation responsive particlesof 'each electrode.

' DESCRIPTION'OF THEPREFERRED I EMBODIMENT Referring to FIG. 1, container 10 is divided into com partments Hand 12 by'means of'an'ion permeable" membrane 14. Preferably, the compartments 11 andl 2 eachcontain a permeable cation'responsive '(colle'ct ing) carbon electrode'andthemembranel l is permeable to anions but not to cations. Two passages 16 and" 17 connect to opposite ends'of compartment 11 and two passages 18 and 19 connect to' opposite ends of compartment 12 Passagesl6 and 18 connect to fourway valve 20 and passages "and 19 connect to four-' way valve; 21. The supply of raw, brackish water in passage 24 isconnected to valve 20 bybranch passage}? and valve passage 26 connects passage to'passage 16 when valve 20 is in the illustratedfull line position. A second branch passage 30 connectsthe raw water sup: ply to passage 19 throughpas 'sage 31 of valve 2l when the valveis in the illustrated full line position.

Passage 17 connects the fluid dischargedfrom com partment 11 to outlet passage 34 through valve passage 35 and passage 18-connects the fluid discharged from compartment 12 with outlet passage 38 thr'o'ughvalve passage 29.

A direct current power supply 44 is connected through reversible switch 45to leads 46 and47 terminating in wires 48 and 4 9, respectively, which'ser've to supply and distribute the electric current to the "electrodes. In the position of theswitch shown in "FIG; 1; the wire 48 is connected to the positive side'of current I supply 44 and wire 49 is connected to the negative side. In the alternate position of the switch, the polarity of wires 48 and 49 is reversed.

In FIG. 2, the compartments 11 and 12 are shown filled with coated carbon particles 50 and 51, respectively, forming the cation responsive carbon electrode in each compartment. The particles are sufficiently packed to be electrically conductive and yet permit the passage of fluid from one end of the compartment to the other. Any sufiiciently porous carbon can be used instead of granular carbon in each electrode compartment and the carbon may or may not be chemically treated to enhance its affinity for cations and may or may not have cation permeable materials deposited within the micropores and upon the extensive surface of the carbon. A treatment of carbon particles to produce cation and anion responsive electrode materials is described in said US. Pat. No. 3,515,664 andcomprises applying cation and anion responsive material in fluid form and then effecting their polymerization on the carbon particles. However, any suitable treatment may be used for granular or porous carbon, or untreated carbon can be used. For instance, cation responsive carbon can be prepared by a two-step process, the first step being carboxylation (or sulfonation) of the extensive carbon surface and the second step con sisting of filling the pore volume of the carbon witha strongly ionized cation exchange resin.

The first step can be accomplished by oxidizing the carbon surfaces using a hot mixture of concentrated sulfuric and nitric acids. This procedure will produce weak acidic carboxylic surface compounds which will in turn: produce a positive charge on the surfaces, reducing the tendency to adsorb anions; enable the electrode to transform farodaic currents associated with electrolysis of water into cation responsiveness by buffering the resulting pH effects; and also by means of buffering capacity, to eliminate deleterious effects such as pH induced precipitation of insoluble carbonates.

The second step can be accomplished by first filling the pores of previously dried carbon with phenolsulfonic acid after which formaldehyde, or successively epichlorohydrin then formaldehyde, can be added prior to curing at elevated temperature. This procedure results in filling the pore volume with a cross linked resin which is permeable to cations but not to anions. Thus the carbon is made cation responsive. Additionally, the resin filled pores are provided with a permanent supporting electrolyte which enhances the current carrying capability when operating in waters of low salinity.

The electron flow is schematically illustrated in FIG. 3 in-which a single particle of each electrode is shown on opposite sides of membrane 14 and connected to opposite sides of the power source 44. it is understood that the fluid flow can be in the same direction or in opposite directions on opposite sides of membrane 14, counter flow being preferred. The salt in the entering water is composed of sodium ions with a positive charge and chlorine ions with a negative charge. When an electric current is sent through the water flowing through the electrodes by closing switch 45, the negative chlorine ions in compartment 12 are drawn through membrane 14 toward the positive electrode particles 50. A chlorine ion 55 is shown passing through membrane 14. This action leaves excessive sodium cations (Na) which are adsorbed by the negative electrode particles 51. The additional electrons'required to maintain electroneutrality are-moved by the power source from particles 50 to particles 51, thereby releasing sodium ions from particles 50 into passage 1 1. However, the released sodium cations cannot pass through membrane 14 toward particles 51. A sodium ion 57 is shown leaving particle 50 and being stopped by membrane 14. The arrow 58 illustrates the direction of electron (e") flow. Thus, it can be seen that sodium and chloride ions are removed from water flowing in compartment 12 thereby producing product water, and that sodium and chloride ions are added to the water flowing in compartment 11 to produce brine. Referring to FIG. 1, the brine leaves compartment 11 through passage 17 and outlet passage 34 and the product water leaves compartment 12 through passage 18 and outlet 38.

in summary, the external power source drives elec- Ytrons (e) into electrode 51 and extracts electrons from the other electrode 50. The electrode 51 adsorbs positively changed ions (cations) and the electrode 50 desorbs an equivalent number of cations. Electroneutrality is maintained by the flow of negatively charged ions (anions) through the anion permeable membrane 14. Thus, the interstitial water within the particles 51 is desalted (demineralized) while the mineralization of the interstitial water within particles 50 is increased. After a suitable period of time during which the respective stream of water through the two compartments are disposed of, the electric current is caused to be reversed by operation of switch 45 and the process is repeated with a corresponding reversal of the desalting effects in the two compartments. The sodium ions which were previously absorbed on particles 51 are now desorbed by particles 51, and sodium ions are now adsorbed by particles 50 so that the compartment 11 now produces product water and compartment 12 produces brine. Switch reversal should take place when the current density has declined with time to an inacceptable level because of the exhaustion of the finite capacity of the electrodes to absorb and desorb cations.-

The direction of the counterflow of water through compartments l1 and 12 can be reversed if desired by simply moving the two-way valves 20 and 21 into their alternate positions in which the passages assume the dashed line positions shown in FIG. 1. This introduces fresh water into the compartment which was previously producing brine and serves to wash the brine from the compartment, after which product water is produced in this compartment.

A stack 59 of electrodes is illustrated in FIG. 4 with one set of alternate electrodes designated Ila-11c and the other set of alternate electrodes designated l2a-12c. The wires 48 for electrodes Ila-11c are con 21, respectively. It is apparent that the number of compartments in stack 59 can be varied to vary the quantity of product water produced.

The structure of the electrodes can be modified by mixing anion exchange resin particles within the macropores or interstitial spacesin the porous carbon tween. the cation responsive particles 51 in space 1 2 andfanioncxchange resin beads 66, are interspersedbetween the; cation responsive particles 501 inspace I-l. The-particles and beads can be loaded alternately into each compartment so thatthe anion responsive beads tend toform layers between the cation responsive particles andsome-of'thebeads move-into the spacesbetween the-particles,1as: illustrated. The electrical leads 481'.and 49 extendalmost.completelythrough the com.-

partments l l and= l 2; respectively in order to provide electricalcontact with-alltheparticles 50 andS-l =in the compartments. The beads. provide-the anions withincreased mobility, to move through the watertoward'themembrane 14, while the cationsmove to the nearby carbon particles. Anions can; go through. the beads faster than-througnwater-i to reachathe. membrane; and: the. beads" do; not-- have to. be in contact to increase. movement-of anions.As.an1example,- thescarbonparticles 50,5 1 and :the :beadsfiS; .661 in'FIG. -5-could be approximately one eighth inch .and-one-sixteenth inch. in diameter, respectively. Theibeadscan be fabricated .of'

plastic material whichis treated'to ,beanion' responsive and canbe;of,any.shape.,ln the event that the electrodes comprise anion' responsive particles and the" membranez-is permeableto cations, then cation responsivebeads would beinterspersedbetween'the anion responsive particles to aid the-movement of cations toward the membrane.

While the operationof the invention hasbeen describedwin connection with .theremoval ofsodium and chloride ions, these ionsare referred to only as illustrative of the operation of'theinvention-since the inventionalsoremoves from brackish water other cations, such-asCaTflMgf, and K and other anions, such as S0,, HCO and N0 It is understood that theelectrode. particlesin compartments 11 and 12,!could :be anion responsive andthemembrane canbe permeable to cations. As illustrated :in FIG. 2a, the particles 70 and =7l 'in chambersll and 12;.respectively, are anion responsive andthemembrane 72' is-permeable to cations; with such an arrangement, cations will flow through the membrane from i one compartment to the other, and "one electrode will absorb anionswhile. theother-electrodewill desorban equivalent number of anions. However, thedegradationof theelectrodes is toward the. cation responsiveformsince an anion respon-,

sive electrode.has aitendencyto change into a cation responsive electrode. Therefore, this-altematearrangement is not .as .desirableasthe first described arrangement of FIGS l -3 which utilizes cationresponsive electrodes.

Conventional electrodialysis uses alarge total voltage imposedacross-a stack of many-membrane pairs so that the membranes arelocated*inseries-across the potential source. When the electrodialysis apparatus is operating-properly, there is substantiallyequal voltagedrop across the 1 plurality .of membranes. However, in the event that scale is deposited on a membrane or a membrane. is .otherwise impaired,a largevoltage drop will occur across this membrane and very little voltagedrop will 'occur acrossthe other membranes,resulting-minevitable destruction of the apparatus. Therefore,con-

. ventional electrodialysis stacks are. potentially unstable "and subject to being damaged or. destroyed. In the present invention,the'electrodesare in parallel in the electric circuit so that there is no possibility ofalarge voltage' becoming imposed across asingle membrane'as the result of flow maldistribution or the deposition of scale on any. membrane of any cell. In the present invention, one badcell does not affect the others and: does not create a situation that accelerates thedestruction of the stack.

" Also, aspreviously indicated, the present invention has the advantage over. theprocess of- US. Pat. No. 3,515,664 in thatit produces double'eflect'ofthe current. Assuming the same current'flow'per unit of'electrode area and the same drivingvoltage', the presentinvention will'produce inthe neighborhood of twice the product water as would be produced with the same amount of power in the patentedprocess since the present invention doesnot require a-separate regenerativestep. Further, the present invention-requires only one kind of carbon electrode whereas the patented process .requirestwo kinds. Therefore, the presentinvention has the advantage. of simplification ofinventory. Also, in the-present invention, the single kind oficarbon electrode. is preferably cation respondingwhich has durability superior to an anion responding: carbon electrode which must also be used in the patented process. The utilizationxof only cation responding electrodes permits-the present invention to operate athigher current densities.

What is claimed as new is: 1'. In an apparatus for demineralizingan electrolyte fluid;

a membrane permeable to eithercations'oranions but not to both; separate compartments on opposite sides of said membrane;

means for connecting each compartmentwith-said electrolyte fluid;

each compartment containing an electrode responsive to counter ions of the opposite'ch'arge to those passing through said'r'nembrane, each-electrode being permeable to permit the flow of'said fluid therethrough; and means for applying a potential across-said-electrodes to cause one electrode to adsorbsaid counter ions and the other electrode to desorb said counter ions; electroneutrality being maintained by the passage-of ions through said membrane, the mineralization of the fluid flowing through the adsorbing-electrode being decreased and the mineralization of the fluid 3. In an apparatus as defined in claim 2 wherein the negative side of said'potential applying means being. connected to the adsorbing electrode and the positive side of said potential applying means beingconnected to the desorbing electrode.

4. In an apparatus as defined in claim 1, said membrane being permeable to cations and said electrodesbeing anion responsive.

5. In an apparatus as defined in claim 2 wherein the negative side of said potential applyingmeans being connected to the desorbing electrode and the positive side of said potential applying means being connected to the adsorbing electrode.

6. In an apparatus as defined in claim 1 wherein each of said electrodes comprise carbon particles to which an ion exchange fluid material is applied and then polymerized to make insoluble.

7. In an apparatus as defined in claim 6 wherein the surface of said particles are first oxidized with an acid mixture.

8. In an apparatus as defined in claim 1 wherein said potential applying means comprises means for reversing the charge applied to said electrodes to reverse the adsorbing and desorbing action of said electrodes.

9. In an apparatus as defined in claim 1 wherein said potential applying means comprises a source of electrical potential, and separate wire terminals extending into each of said electrodes and connected to opposite sides of said potential source.

10. In an apparatus as defined in claim 1 wherein said connecting means comprise valve means for flowing said fluid in one direction through one of said electrodes and in the opposite direction through the other electrode.

11. In an apparatus as defined in claim 1 wherein each of said electrodes comprises particles having beads interspersed therebetween responsive to ions of the same charge as pass through said membrane.

12. In an apparatus as defined in claim 2 wherein each of said electrodes comprises cation responsive particles, and anion exchange beads smaller than said particles and interspersed between said particles to increase the mobility of anions toward said membrane.

13. In an apparatus as defined in claim 11 wherein said particles and beads are disposed in said compartment in substantially layer form with said beads also interspersed between said particles.

14. In an apparatus as defined in claim 13 wherein said potential applying means comprises a wire terminal in each compartment, each terminal being in electrical contact with all said particles in said compartment.

15. Inan apparatus as defined in claim 1 wherein said connecting means comprise valve means for reversing the direction of flow of said fluid through said electrodes.

16. In an apparatus as defined in claim 1 having a plurality of membranes in addition to said one membrane to form a stack of membranes, each of said membranes having a compartment on each side thereof containing a permeable electrode responsive to counter ions, means for connecting all said compartments to said fluid, said potential applying means comprising a plu rality of positive terminals connected in parallel to all the electrodes in a set on one side of said membranes and a plurality of negative terminals connected in parallel to all the electrodes in another set on the other side of said membranes.

17. In an apparatus as defined in claim 16 wherein said potential applying means comprises means for reversing the charge on said electrodes.

18. In an apparatus as defined in claim 16 wherein said connecting means comprise valve means for reversing the direction of flow of said fluid through all of said electrodes. 

2. In an apparatus as defined in claim 1, said membrane being permeable to anions and said electrodes being cation responsive.
 3. In an apparatus as defined in claim 2 wherein the negative side of said potential applying means being connected to the adsorbing electrode and the positive side of said potential applying means being connected to the desorbing electrode.
 4. In an apparatus as defined in claim 1, said membrane being permeable to cations and said electrodes being anion responsive.
 5. In an apparatus as defined in claim 2 wherein the negative side of said potential applying means being connected to the desorbing electrode and the positive side of said potential applying means being connected to the adsorbing electrode.
 6. In an apparatus as defined in claim 1 wherein each of said electrodes comprise carbon particles to which an ion exchange fluid material is applied and then polymerized to make insoluble.
 7. In an apparatus as defined in claim 6 wherein the surface of said particles are first oxidized with an acid mixture.
 8. In an apparatus as defined in claim 1 wherein said potential applying means comprises means for reversing the charge applied to said electrodes to reverse the adsorbing and desorbing action of said electrodes.
 9. In an apparatus as defined in claim 1 wherein said potential applying means comprises a source of electrical potential, and separate wire terminals extending into each of said electrodes and connected to opposite sides of said potential source.
 10. In an apparatus as defined in claim 1 wherein said connecting means comprise valve means for flowing said fluid in one direction through one of said electrodes and in the opposite direction through the other electrode.
 11. In an apparatus as defined in claim 1 wherein each of said electrodes comprises particles having beads interspersed therebetween responsive to ions of the same charge as pass through said membrane.
 12. In an apparatus as defined in claim 2 wherein each of said electrodes comprises cation responsive particles, and anion exchange beads smaller than said particles and interspersed between said particles to increase the mobility of anions toward said membrane.
 13. In an apparatus as defined in claim 11 wherein said particles and beads are disposed in said compartment in substantially layer form with said beads also interspersed between said particles.
 14. In an apparatus as defined in claim 13 wherein said potential applying means comprises a wire terminal in each compartment, each terminal being in electrical contact with all said particles in said compartment.
 15. In an apparatus as defined in claim 1 wherein said connecting means comprise valve means for reversing the direction of flow of said fluid through said electrodes.
 16. In an apparatus as defined in claim 1 having a plurality of membranes in addition to said one membrane to form a stack of membranes, each of said membranes having a compartment on each side thereof containing a permeable electrode responsive to counter ions, means for connecting all said compartments to said fluid, said potenTial applying means comprising a plurality of positive terminals connected in parallel to all the electrodes in a set on one side of said membranes and a plurality of negative terminals connected in parallel to all the electrodes in another set on the other side of said membranes.
 17. In an apparatus as defined in claim 16 wherein said potential applying means comprises means for reversing the charge on said electrodes.
 18. In an apparatus as defined in claim 16 wherein said connecting means comprise valve means for reversing the direction of flow of said fluid through all of said electrodes. 